Four-wheel drive and all-wheel drive vehicles are equipped with differentials and/or viscous couplings that are designed to allow momentary differences in wheel speeds when the vehicle turns a corner or temporarily spins a tire. However, if the differentials or viscous couplings are forced to operate 100% of the time because of mismatched tires, they will experience excessive heat and unwarranted wear until they fail.
This makes maintaining the vehicle manufacturer's recommended tire inflation pressures and using matched tires on all wheel positions necessary procedures to reduce strain on the vehicle's driveline. Using matched tires means all four tires are the same brand, design and tread depth. Mixing tire brands, tread designs and tread depths may cause components in the vehicle's driveline to fail.
What does a driver do if one tire has to be removed from service when it and the other three tires have already worn between two-thirds to one-half of their original tread depth? Simply installing one new tire runs the risk of drivability problems or expensive driveline damage. Replacing the other three partially worn tires along with the damaged tire significantly increases the cost.
Tire Rack can provide a solution by matching the tread depth of the replacement tire to the tread depth of the partially worn tires that will remain on the vehicle by removing tread rubber from a new tire on a specialized machine that operates as a tire lathe (shaving a tire). While this may seem counterintuitive, the value of the mileage sacrificed by the one replacement tire is considerably less than the cost of rebuilding worn driveline components.
Tire Rack's tire shaving service is primarily used to prepare competition tires for race track use. This same service can also be used to remove tread rubber from new pairs or individual street tires used on four-wheel drive and all-wheel drive vehicles to allow them to match the remaining tread depth of the other partially worn tires that will remain on the vehicle. In addition to providing equivalent tread depth to eliminate driveline stress, shaved tires will also better match the traction and handling qualities of the remaining worn tires.
While the cost of our street tire shaving service will range from $25 to $35 for each tire, it is significantly less than the cost of unnecessarily replacing the remaining two or three good tires with lots of mileage still available from them.
The following are recommendations from three manufacturers for matching the tires used on their four-wheel drive and all-wheel drive vehicles.
| Manufacturers Recommendations | |
|---|---|
| Audi | As published in their vehicle owner's manual, "rolling radius of all four tires must remain the same" or within 4/32-inch of each other in remaining tread depth. |
| Porsche | Cayenne within 30% of the other tire on the same axle's remaining treadwear. |
| Subaru | Within 1/4-inch of tire circumference or about 2/32-inch of each other in remaining tread depth. |
Additional recommendations from other Original Equipment vehicle manufacturers may be found in the owner's manual, by contacting your local vehicle service department or the manufacturer directly.
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